PdO x /Pd at Work in a Model Three-Way Catalyst for Methane Abatement Monitored by Operando XANES

Matam, Santhosh ; Chiarello, Gian ; Lu, Ye ; Weidenkaff, Anke ; Ferri, Davide

In: Topics in Catalysis, 2013, vol. 56, no. 1-8, p. 239-242

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    Summary
    The oxidation state of palladium in a model Pd/ACZ three-way catalyst was monitored by synchronous XANES and mass spectrometry during two consecutive heating (to 850°C) and cooling (to 100°C) cycles under stoichiometric conditions simulating exhaust after treatment of a natural gas engine. During heating in the first cycle, PdO reduction occurred around 500°C and the initial fully oxidized state of Pd was never recovered upon heating and cooling cycles. A mixed Pd2+/Pd oxidation state was at work in the second cycle. Hence, the operando XANES study reveals that the PdO x /Pd pair exists in a working catalyst but is less active than the catalyst in its initial state of fully oxidized palladium. It is also evident from XANES spectra that ceria-zirconia promotes re-oxidation of metallic Pd, thus reasonably sustaining catalytic activity after exposure to high temperatures